This project investigates novel genetic control mechanisms for meiosis and recombination in mammals. Previously, we used forward and reverse genetic approaches in mice to identify genes that function in key aspects of meiosis: recombination initiation, prophase I transcriptional regulation, noncrossover recombination, the DNA damage checkpoint, and crossing over. This proposal seeks to extend investigations in three areas where the mammalian genetic determinants are poorly understood. Aim 1 concentrates on a separation-of- function allele of the transcription factor MYBL1 (A-MYB) that specifically causes male meiotic arrest due to prophase I defects in meiotic chromosome metabolism, including a lack of crossing over. The role of MYBL1 in regulating the male meiotic transcriptional program will be characterized by linking gene expression aberrations to direct gene targets. Aim 2 pursues findings form studies of mice bearing a mutant allele of Trip13, the ortholog of yeast PCH2 (pachytene checkpoint 2). Unlike the yeast and worm orthologs, TRIP13 has no apparent meiotic checkpoint function;rather, it appears to affect noncrossover recombination. This will be tested directly by in vivo analysis of recombination products at a hotspot. Remarkably, we observed that ablation of the small synaptonemal complex (SC) component SYCP3 could bypass the early meiotic death of oocytes mutated for either Trip13 or Dmc1, the meiotic recA homolog that is required for interhomolog recombinational repair of double strand breaks (DSBs). Since SYCP3 is a phosphoprotein with consensus targets ([S/T]Q) of the ATM/ATR DNA damage surveillance kinases, genetic and molecular experiments will be performed to test whether: 1) SYCP3 is an essential component of the meiotic DNA damage checkpoint;or 2) it plays a role in governing recombination partner choice (sister chromatid vs homologous chromosome). Other potential SC components will also be evaluated for such activities. The topic of Aim 3 is a mutation called Mei4 that is an allele of cyclin B1 interacting protein 1 (Ccnb1ip1). This allele causes the specific phenotype of eliminating crossing-over in both sexes. While CCNB1IP1 has a RING domain characteristic of ubiquitin E3 ligases, studies of interacting proteins suggest that it also/instead functions as a SUMO ligase. Experiments are proposed to test this idea, and to understand how this activity is required for meiotic crossing over. PUBLIC HEALTH RELEVANCE: Meiosis is a unique, specialized cell division process that generates a single set of chromosomes carried by eggs and sperm. The proper execution of meiosis is essential for fertility and normal development of conceptuses. It involves recombination, which must occur accurately to yield gametes with a normal number of chromosomes. Errors in this process are common causes of birth defects. This project investigates several aspects of meiosis, including genetic recombination and quality-control processes that govern and monitor it.